#define  _CRT_SECURE_NO_WARNINGS 1


https://leetcode.cn/problems/flood-fill/
class Solution {
    typedef pair<int, int> PII;

    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { 1,-1,0,0 };

public:
    vector<vector<int>> floodFill(vector<vector<int>>& image, int sr, int sc, int color) {
        int prev = image[sr][sc];
        if (prev == color) return image;

        int m = image.size(), n = image[0].size();

        queue<PII> q;
        q.push({ sr,sc });
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            image[a][b] = color;
            for (int i = 0; i < 4; i++)
            {
                int x = a + dx[i], y = b + dy[i];
                if (x >= 0 && x < m && y >= 0 && y < n && image[x][y] == prev)
                {
                    q.push({ x,y });
                }
            }
        }
        return image;
    }
};


https://leetcode.cn/problems/number-of-islands/
class Solution {
    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { -1,1,0,0 };
    bool vis[301][301];
    int m, n;
public:

    void bfs(vector<vector<char>>& grid, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i,j });
        vis[i][j] = true;
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && vis[x][y] == false)
                {
                    q.push({ x,y });
                    vis[x][y] = true;
                }
            }
        }

    }

    int numIslands(vector<vector<char>>& grid) {
        m = grid.size();
        n = grid[0].size();
        int ret = 0;
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (grid[i][j] == '1' && vis[i][j] == false)
                {
                    bfs(grid, i, j);
                    ret++;
                }
            }
        }
        return ret;
    }
};

https://leetcode.cn/problems/max-area-of-island/submissions/646881168/
class Solution {
    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { -1,1,0,0 };
    bool vis[51][51];
    int m, n;
public:
    int bfs(vector<vector<int>>& grid, int i, int j)
    {
        int ret = 0;
        queue<pair<int, int>> q;
        q.push({ i,j });
        vis[i][j] = true;
        ret++;
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 1 && vis[x][y] == false)
                {
                    q.push({ x,y });
                    vis[x][y] = true;
                    ret++;
                }
            }
        }
        return ret;
    }
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m = grid.size();
        n = grid[0].size();
        int ret = 0;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (grid[i][j] == 1 && vis[i][j] == false)
                    ret = max(ret, bfs(grid, i, j));
        return ret;
    }
};

https://leetcode.cn/problems/surrounded-regions/description/
class Solution {
    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { -1,1,0,0 };
    int m, n;
public:
    void bfs(vector<vector<char>>& board, int i, int j)
    {
        queue<pair<int, int>> q;
        q.push({ i,j });
        board[i][j] = '.';
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O')
                {
                    q.push({ x,y });
                    board[x][y] = '.';
                }
            }
        }

    }
    void solve(vector<vector<char>>& board) {
        m = board.size();
        n = board[0].size();
        for (int i = 0; i < m; i++)
        {
            if (board[i][0] == 'O') bfs(board, i, 0);
            if (board[i][n - 1] == 'O') bfs(board, i, n - 1);
        }
        for (int j = 0; j < n; j++)
        {
            if (board[0][j] == 'O') bfs(board, 0, j);
            if (board[m - 1][j] == 'O') bfs(board, m - 1, j);
        }
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (board[i][j] == 'O')
                    board[i][j] = 'X';
                else if (board[i][j] == '.')
                    board[i][j] = 'O';
            }
        }

    }
};